Ali Abdallah Saleh’s return to Sanaa takes Yemen to the brink of civil war. Chaos on the Arabian Peninsula’s southern tip is dangerous for the Saudis and America and good news for al Qaeda. Saleh has licked his wounds in Saudi Arabia since he survived an assassination attempt in June. Now he’s back.

His sons and relatives have held on to parts of the capital and elements of the Army, waiting for this moment of return. Rival warlords have seized other parts of both the country and the Army, and peaceful demonstrators have grabbed other slices of the capital and the country. The economy has collapsed. Unemployment is now more than 40 percent. Division Gen. Ali Muhsen al-Ahmar, the rebel commander of the First Armored, and Saleh’s oldest son, Ahmed, who commands the Republican Guard, now are poised to start a full-scale civil war. Both are well armed.

The Saudis, who give almost every Yemeni politician bribes, have botched managing this crisis from the start. They lead the Gulf Cooperation Council political process that has tried to talk Saleh out of office, and he has made them look like fools. They are deeply ambivalent about Saleh, whom they have tried to oust in the past. But Saleh has also provided stability in their neighborhood for years. The Saudis don’t like revolutions, especially next door, and they have never been very good at managing Yemeni affairs. They treat the Yemenis with contempt, and the Yemenis reciprocate.

American diplomacy has tried to help the Saudis without becoming responsible for Yemen. We wisely don’t want to take on the burden of caring for the Arab world’s poorest country, which is running out of everything: oil, water, arable land, and hope. With a fast-growing population that will double to 40 million by 2030, a nearly universal drug addiction to qat, and no jobs, Yemen brings new meaning to the idea of a failing state. Saudi Arabia, Qatar and the U.A.E. have the money to help and have given generously in the past. This should remain their problem.

Saleh and his kids are like all autocrats: they don’t want to give up power. They can see what happens to Arab dictators and their sons when they quit—exile, imprisonment, or death. The rebels, both generals and democrats, know what will happen if Saleh prevails—exile, imprisonment, or death. Al Qaeda in the Arabian Peninsula and other dissident groups like the Shia Houthi rebels are the winners for now. There is less and less state authority in their strongholds.

AQAP’s bombmakers—the best al Qaeda has ever produced—can perfect their wares with less and less fear of Saleh’s security forces. Since AQAP has sent bombs to hit Detroit (2009) and Chicago (2010) already, it is no wonder the U.S. counterterrorist community is deeply worried. AQAP has also tried to kill Saudi Arabia’s counterterror maestro, Prince Muhammad, four times, so the Saudis are worried, too. Three million barrels of oil sail on tankers past Yemen every day, so the world should be worried.

Drones have hurt AQAP in the past, but they also antagonize Yemenis and swell the ranks of AQAP recruits. AQAP’s adept propaganda exploits the drone war as evidence that al Qaeda is fighting a foreign enemy that kills innocents.

The United States needs to build capacity to fight AQAP—alone if we have to—but above all we need an effective Yemeni partner. That is nowhere in sight.